The current implementation of `getBabelrc` doesn't consider [`env` option of .babelrc](https://babeljs.io/docs/usage/babelrc/), which causes an error when a project has extract-react-intl-specific settings under `env` option.
This commit fixes the above problem by properly handling `env` option using the values of BABEL_ENV, NODE_ENV.

It could be debatable whether this is dealt with by read-babelrc-up or this package, but I believe the former should return the exact content of .babelrc without any modifications or merges, so I've forked this package.

The `removePrefix` option seems to be period-separated rather than slash-separated if you look at how `removePrefix` is implemented in [react-intl-auto](https://github.com/akameco/babel-plugin-react-intl-auto/blob/master/src/index.js#L47).

Consider env values when parsing .babrlrc

chore(npm): update

The user can now choose to use babel 6 or babel 7.

chore: make babel-core a peer dependency

feat: Drop node v6

refactor(deps): update babel7

Allow to specify custom module name passed to babel-plugin-react-intl

…64e058f849'

git-subtree-dir: extract-react-intl
git-subtree-mainline: 698f1ed
git-subtree-split: 64f6800